Up to the present day, the primary design objective in the manufacture of household toilets in the United States has been to deliver the same fixed volume of water during each flush, sufficient to completely remove any typical solid or liquid waste that may be deposited in the toilet bowl. The standard toilet consists of a water tank and a valve that releases essentially the full volume of water in the tank into the toilet bowl. Pressing the external flush handle lifts a buoyant flapper-type (or bulb-type) valve that is located along the bottom of the tank. This standard flushing approach offers simplicity and cost savings in construction and manufacture, while at the same time meeting essentially all toilet waste removal demands of the typical household. However, because liquid waste removal in particular, and often solid waste removal as well, requires only a fraction of the water stored in the toilet tank, the single-flush design results in a significant waste of water.
With increasing emphasis placed on water conservation in the past decades, “dual-flush” toilets have become an increasingly available option in the market targeting household consumers. Such toilets allow users to select between a “full” flush using the complete volume of water in the tank and a “partial” flush (for liquid waste, for example) that requires only a partial volume of water for adequate waste removal. These toilets, while more complicated in design and cost, can offer significant savings in water consumption, reducing homeowner utility costs in the long run and particularly benefiting regions and localities facing water shortages.
While dual-flush toilets substantially eliminate the wasteful water consumption associated with the currently prevailing single-flush toilet design, consumers face significant disincentives to utilizing them. Even for those households that wish to contribute to the water conservation effort, the purchase and installation price of a dual-flush toilet can be substantial, up to three times the cost of a standard toilet, or more. In addition, for the typical household, the return on investing in a dual-flush toilet could take years of cost savings through water conservation. Also, any interest in benefitting from a dual-flush toilet is likely diminished by the fact that the household's current standard toilet meets their toileting needs equally well, albeit with less efficiency in water usage.
In response to the growing interest in water conservation, and given the still limited and costly consumer choices for alternative dual-flush toilets, a number of designs for modifying the standard single-flush toilet have been proposed. These designs generally fall within two classes of prior art. The first class includes designs requiring substantial modification or replacement of existing structures within the standard single-flush toilet, while the second class comprises retrofit kits require little or no modification or replacement of the standard flushing components. A common drawback of the first class of designs is the need for tools and a mechanical ability that most households do not possess or care to acquire. An example of such a design is proposed in U.S. Pat. No. 3,795,016, entitled “Toilet Water Tank with Light and Heavy Flush Control”, issued to E. A. Eastman on Mar. 5, 1974. In this arrangement, the single water outlet valve at the base of a standard toilet tank is replaced by a set of two valves, positioned at different water levels within the tank. Opening only the upper valve results in a partial flush, thus limiting the quantity of water released into the toilet bowl. This dual valve design type also requires an accompanying linkage system to selectively open the two valves, with design variations involving either the single handle of the standard toilet, or requiring the use of two separate handles. This particular design has the additional disadvantage of reducing the water column above the elevated partial flush valve, thereby reducing the water pressure available for efficiently removing wastewater from the toilet bowl. As a result, more water may be required to efficiently remove liquid waste.
The second class of prior art designs (comprising add-on kits that retrofit onto existing single-flush toilets) require little or no modification to the existing structures. However, these designs generally suffer from one or more of the following drawbacks: a) many are of complex design and are therefore more costly to manufacture; b) require tools to install; c) are difficult to retrofit onto standard toilet components; d) offer operational reliability for only a limited variety of single-flush architectures; e) offer limited water conservation, even during reliable operation; and/or f) require the toilet user to learn and apply a new procedure for flushing the toilet.
One exemplary retrofit design type involves the installation of a dual-flush linkage connected to the standard flush handle. This arrangement is disclosed in U.S. Pat. No. 5,319,809, entitled “Dual Mode Flush Mechanism for Toilets”, issued to E. J. Testa on Jun. 14, 1994. In this case, Testa proposes a mechanism that allows a full flush by pressing the handle downward in the normal fashion for solid waste removal, while pulling upward on the handle to initiate a partial flush, the upward motion going toward a preset stop point that partially opens the flapper-type valve at the base of the water tank. Since the partial lifting of the flapper-type valve prevents its buoyant tendency to float as the water level reaches the bottom of the tank, releasing the flush handle immediately re-seats the valve. Therefore, the amount of water consumed by the flushing action is controlled by the user. However, this design approach suffers from a number of drawbacks. In particular, the Testa mechanism consists of a double-cam and lever system containing multiple moving parts, limiting its economy of manufacture. Additionally, installation requires tools and the disassembly of the standard handle linkage. Also, since the Testa partial flush method relies on incompletely opening the water-release flapper-type valve, the water pressure available from the water column above the flapper-type valve is not fully utilized for efficiently removing wastewater from the toilet bowl. Consequently, more water in the tank may need to be released to effective removal of the liquid waste.
Variants on this design approach replace the complex cam linkage system with a simpler stop-point mechanism that incompletely opens the flapper-type valve for both partial and full flush operation. The toilet user simply presses and holds down the toilet handle for a longer period of time to achieve a full flush. However, in this design approach, the full flush (as well as the partial flush) fails to utilize the full water pressure head available above the valve. As a result, the removal of solid waste (which is especially reliant on a high-pressure flush) also requires excess water usage and may fail to completely evacuate the waste from the toilet bowl. Additionally, the toilet no longer operates in its stand manner in that the standard full flush is no longer automated with a simple press and release of the handle. This approach therefore requires relearning and additional effort by household members, and can be confusing to household guests.
Other retrofit design concepts rely upon the premature removal of the flapper-type valve's buoyancy to halt the water flow from the tank and into the bowl, and thereby achieve a partial flush. For example, U.S. Pat. No. 4,945,580 entitled “Volume-Selective Water Closet Flushing System” and issued to M. M. Schmitt et al. on Aug. 7, 1990, proposes a flexible tube that is inserted into the buoyant chamber of the flapper-type valve, with the other end fixed to a pressure release valve above the water level. The air tube assembly is accompanied by an installed linkage between the flush handle and the valve system, allowing the user to selectively activate the air tube passageway for a partial flush by pressing the toilet handle in the prescribed manner. When a partial flush is selected, the pressure release valve opens and thereby allows the water pressure at the level of the flapper-type valve to force the air from the buoyant chamber out through the tube, filling the chamber with water and causing the valve to fall back down into its closed position. Depending on the prior art variations within this design concept, drawbacks can include component complexity and installation requirements for the linkage, valving, and tube components. Additionally, the weight, placement, elasticity, and position of the air tube attached to the flapper-type valve can unbalance the valve's buoyant force that regulates its proper closure.
Other prior art retrofit designs rely on mechanical rather than hydraulic methods for automatically closing the flapper-type valve prematurely at a preset water level to achieve a partial flush. For example, the arrangement disclosed in U.S. Pat. No. 4,117,556 entitled “Flush Water Conserver” and issued to O. A. Semler on Oct. 3, 1978, suspends a downwardly-slidable float unit above the water release valve. With the appropriate manipulation of the flush handle, a latching system either allows the float to descend and prematurely force the water release valve closed, or instead prevents the float's descent to allow a full flush to complete. The Semler design requires several linkages and moving parts, reducing its economy of manufacture and reliability of operation. Additionally, as with all designs that allow for only two preset levels of water usage, the degree of water conservation achieved is limited during the removal of solid waste. While nearly all liquid waste deposits can be efficiently removed with a single pre-selected volume of water for the partial flush, the amount of water required to efficiently remove solid waste varies depending on the consistency, amount and size of solid waste matter deposited, and is often less than the amount used in a full flush. Consequently, one pre-set full flush volume often uses excessive amounts of water. It is also been found that the minimal partial flush water volume associated with the removal of liquid waste is often more than sufficient for also removing solid waste material. In general household practice, the amount of water required for solid waste removal will vary between the minimal required for liquid waste removal and the full flush volume. Consequently, prior art dual-flush designs offering only a single preset full flush volume will often consume more water than required in solid waste removal.
Another class of retrofit devices addresses the problem of excess water usage during solid waste removal by giving the toilet user full operational control in closing, as well as opening, the flapper-type water valve. In these designs, the act of lifting the toilet handle lifts open the valve, while releasing or moving the handle in the opposite direction replaces the valve in its closed position. The toilet user can select any volume of water for eliminating liquid or solid waste. In addition, these designs eliminate design complexity by avoiding multiple-component linkage systems intervening between the toilet handle and the flapper-type valve, often replacing them with a direct rigid connection. For example, U.S. Pat. No. 4,536,900 entitled “Water Conserving Flush Valve for Toilets” issued to G. P. Hayes on Aug. 27, 1985 proposes a cable attachment from the flush handle arm to a lever resting above the flapper-type valve. Pressing the handle lifts the valve in the standard manner, while returning the handle to its resting position lowers the level via cable connection to press the valve closed. However, while this design avoids the complex linkages of the previously-described prior art, it does require correct placement of several components at multiple attachment points, as well as several moving parts, and further includes an awkwardly-placed cable conduit that can impede reliable valve control. U.S. Pat. No. 4,388,736 entitled “Tank Flushing Means” and issued to P. V. Roosa on Jun. 21, 1983 proposes an alternative arrangement using a single rod connecting the flush handle arm directly to the flapper-type valve. Attached to the rod is a float resting directly above the valve to counteract the added weight of the device and flush handle arm, such that buoyancy is maintained when the handle is released for a full flush. This design also suffers from a number of flaws. Many flapper-type valves do not have an eyelet for attachment to the hooked end of the rod, making installation difficult or impractical, especially for valves made of hard plastic at this connection point. Additionally, because the float rests above the valve, buoyancy is lost at water level higher than that reached in a standard full flush, resulting in an incomplete full flush. Additionally, the design operates reliably only for standard toilet designs that allow the control rod to be connected to the toilet handle arm directly above the flapper-type valve. To the extent that the flush handle deviates from this direct position, the downward force of the rod pushes obliquely on the valve, causing improper valve seating or complete valve failure. US Patent Publication 2009/0126094 entitled “User-Controlled Water Saving Toilet”, authored by S. G. Laube and published on May 21, 2009 proposes several types of direct linkage between the flush handle and the flapper-type valve, including chain links, rigid bars, rigid tubes, springs and various combinations thereof. However, these approaches are subject to the same drawbacks of lost full-flush buoyancy and oblique force against the flapper-type valve.